From 9f95f663d40d726345aa1348ec647fa5ced72ef6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Laura=20Kl=C3=BCnder?= <laura@codingcatgirl.de>
Date: Sat, 24 Aug 2024 15:27:31 +0200
Subject: [PATCH] intercept changeset m2m changes

---
 src/c3nav/editor/changes.py | 47 +++++++++++++++++++++++++++++++++----
 1 file changed, 43 insertions(+), 4 deletions(-)

diff --git a/src/c3nav/editor/changes.py b/src/c3nav/editor/changes.py
index 5f6e2a26..0f137d95 100644
--- a/src/c3nav/editor/changes.py
+++ b/src/c3nav/editor/changes.py
@@ -7,7 +7,7 @@ from typing import TypeAlias, Literal, Annotated, Union, Type, Any
 from django.core import serializers
 from django.db import transaction
 from django.db.models import Model
-from django.db.models.fields.related import OneToOneField, ForeignKey
+from django.db.models.fields.related import OneToOneField, ForeignKey, ManyToManyField
 from django.utils import timezone
 from pydantic import ConfigDict, Discriminator
 from pydantic.fields import Field
@@ -88,7 +88,6 @@ ChangeSetChange = Annotated[
 class ChangeSetChanges(BaseSchema):
     prev_reprs: dict[ObjectReference, str] = {}
     prev_values: dict[ObjectReference, FieldValuesDict] = {}
-    prev_m2m: dict[ObjectReference, dict[str, list[int]]] = {}
     changes: list[ChangeSetChange] = []
 
 
@@ -167,8 +166,48 @@ class ChangesetOverlayManager:
         from pprint import pprint
         pprint(self.changes)
 
-    def handle_m2m_changed(self, sender: Type[Model], instance: Model, **kwargs):
-        pass
+    def handle_m2m_changed(self, sender: Type[Model], instance: Model, action: str, model: Type[Model],
+                           pk_set: set | None, reverse: bool, **kwargs):
+        if reverse:
+            raise NotImplementedError
+
+        if action.startswith("pre_"):
+            return self.handle_pre_change_instance(sender=instance._meta.model, instance=instance)
+
+        for field in instance._meta.get_fields():
+            if isinstance(field, ManyToManyField):
+                break
+        else:
+            raise ValueError
+
+        ref = ObjectReference.from_instance(instance)
+        pre_change_values = self.pre_change_values.pop(ref, None)
+        if pre_change_values:
+            self.changes.prev_values[ref] = pre_change_values
+
+        match(action):
+            case "post_add":
+                self.changes.changes.append(AddManyToManyChange(
+                    obj=ref,
+                    field=field.name,
+                    values=list(pk_set),
+                ))
+
+            case "post_remove":
+                self.changes.changes.append(RemoveManyToManyChange(
+                    obj=ref,
+                    field=field.name,
+                    values=list(pk_set),
+                ))
+
+            case "post_clear":
+                self.changes.changes.append(ClearManyToManyChange(
+                    obj=ref,
+                    field=field.name,
+                ))
+
+        from pprint import pprint
+        pprint(self.changes)
 
 
 def handle_pre_change_instance(sender: Type[Model], **kwargs):